Polar bears fur consists of a dense, insulating undercoat topped by guard hairs of various lengths. Polar bears do appear white to us. But there is more to this than meets the eye! Polar bears appear white, but their fur is not white. Each hair is made of keratin, the same substance found in our fingernails and hair.

However, polar bear fur is transparent with a (air–filled) hollow core. Reflection of the sunlight from the densely packed transparent hairs makes polar bears seem to be white. The keratin that makes most of the sun's rays reach their black skin to absorb heat and which in turn provides extra warmth for the skin. The bear's stark white coat provides camouflage in surrounding snow and ice.

Scientists used to think that polar bear's hollow hairs acted like fiber optic tubes and conducted light to their black skin. In 1988, Daniel W. Koon, a physicist and graduate assistant, Reid Hutchins, proved this false. Their experiments showed that a one–fifth inch strand of polar bear hair conducted less than a thousandth of a percent of applied ultraviolet light. So, the black skin absorbs very little ultraviolet light. Instead, Koon believes keratin, a basic component of the hair, absorbs the ultraviolet light.